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운전조건 변화에 따른 이산화탄소 열펌프의 냉난방 성능특성 비교
조홍현(Honghyun Cho),백창현(Changhyun Baek),이응찬(Eungchan Lee),강훈(Hun Kang),김용찬(Yongchan Kim) 대한기계학회 2008 大韓機械學會論文集B Vol.32 No.6
Since operating conditions are significantly different for heating and cooling mode operations in a CO₂ heat pump system, it is difficult to optimize the performance of the CO₂ cycle. In addition, the performance of a CO₂ heat pump is very sensitive to outdoor temperature and gascooler pressure. In this study, the cooling and heating performances of a variable speed CO₂ heat pump with a twin-rotary compressor were measured and analyzed with the variations of EEV opening and compressor frequency. As a result, the cooling and heating COPs were 2.3 and 3.0, respectively, when the EEV opening was 22%. When the optimal EEV openings for heating and cooling were 28% and 16%, the cooling and heating COPs increased by 3.3% and 3.9%, respectively, over the COPs at the EEV opening of 22%. Beside, the heating performance was more sensitive to EEV opening than the cooling performance. As the compressor speed decreased by 5 Hz, the cooling COP increased by 2%, while the heating COP decreased by 8%.
냉매 R1234yf 적용 자동차용 에어컨 Drop-in 성능 특성
조홍현(Honghyun Cho),이호성(Hoseong Lee),박차식(Chasik Park) 대한설비공학회 2012 설비공학 논문집 Vol.24 No.12
In this study, the performance of mobile air conditioner(MAC) systems to which the refrigerants R134a and R1234yf were used was evaluated to compare the characteristic of automotive refrigeration cycles with refrigerant. The experimental setup of a MAC consists of an belt driven compressor, a condenser, an evaporator and a block type thermal expansion valve. The drop-in test on MAC were carried out under variable compressor speed from 800 to 2500 rpm. Performance test by using R1234yf and R134a in the same system revealed low the charge amount and mass flow rates for using R1234yf, that is, up to 10% and 17%, respectively. The compressor discharge temperature of R1234yf is 8℃ lower than that of R134a. The cooling capacity with R1234yf system decreased by 4~7% compared with R134a system. In addition, The COP of R1234yf system is lower 3~4% than that of R134a system.
이단압축을 이용한 이산화탄소 사이클의 냉방성능에 관한 연구
조홍현(Honghyun Cho),류창기(Changgi Ryu),김용찬(Yongchan Kim),조성욱(Sungwook Cho) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
To improve of the cooling performance of a CO₂ cycle, a CO₂ air-conditioner using two-stage compression cycle was tested with a variation of compressor frequency ratio. The cycle options include a basic cycle, a cycle with an intercooler, a cycle with an IHX(internal heat exchanger), and a cycle with an intercooler and IHX. The results show that the cycles with the intercooler, IHX, and intercooler and IHX improved the cooling performance significantly at all frequency ratios. The cycle with the intercooler, the cycle with the IHX and the cycle with the intercooler and IHX improved the cooling COP by 7, 12, and 15% over the basic CO₂ cycle.
트윈로터리 압축기 적용 냉방 및 급탕 겸용 이산화탄소 시스템의 성능특성에 관한 연구
조홍현(Honghyun Cho),이호성(Hosung Lee),백창현(Changhyun Baek),김용찬(Yongchan Kim),조성욱(Sungwook Cho) 대한설비공학회 2008 설비공학 논문집 Vol.20 No.4
The objective of this paper is to investigate the performance characteristics of a CO₂ cooling and water heating system using a twin-rotary compressor with the compression volume ratio of 0.6. The cooling performances of the CO₂ heat pump were measured and analyzed with the variations of charge amount, EEV opening, and compressor frequency. In addition, the performance of the combined system including cooling and water heating was also measured and analyzed by varying inlet temperature of the EEV. As a result, the optimal normalized charge and cooling COP in the cooling mode were 0.307 and 2.06, respectively. The application of the water heating into the CO₂ heat pump improved the cooling performance over 78% and decreased the EEV inlet temperature by 8℃, which can increase system reliability.
R134a 및 R1234yf 적용 냉동시스템의 비가역성 분석
조홍현(Honghyun Cho),이호성(Hoseong Lee),박차식(Chasik Park) 대한설비공학회 2013 대한설비공학회 학술발표대회논문집 Vol.2013 No.6
In this study, the performance of mobile air conditioner(MAC) systems to which the refrigerants R134a and R1234yf were used was evaluated to compare the characteristic of automotive refrigeration cycles with refrigerant. The drop-in test on MAC were carried out under variable compressor speed from 800 to 2500 rpm. Performance test by using R1234yf and R134a in the same system revealed low the charge amount and mass flow rates for using R1234yf, that is, up to 10% and 17%, respectively. The irreversiblilty of evaporator in a R134a air conditioning system with compressor speed under idle condition was 36.8% which was maximum value, and that of compressor increased with compressor speed. The irreversibility of compressor and IHX in a R1234yf air conditioning system with IHX with compressor speed was 39.6%, 3.6% under idle condition, and those was 44.1%, 9.7% at the compressor speed of 2520 rpm.
R1234yf와 R134a 냉매의 이젝터를 적용한 냉동사이클 성능에 대한 해석적 연구
조홍현(Honghyun Cho),박차식(Chasik Park) 대한설비공학회 2015 설비공학 논문집 Vol.27 No.7
This paper presents a numerical study on the performance of a vapor compression cycle equipped with an ejector as an expansion device to improve the COP by reducing the expansion loss and compressor work. The simulation is carried out using a model based on the conservation of mass, energy and momentum in the ejector. From the results of the simulation, the vapor compression cycle equipped with an ejector showed a maximum COP improvement of 14.0% when using R134a refrigerant and 16.8% when using R1234yf. In addition, the performance of the system with an ejector represents the increased performance as the temperature difference between condensing and evaporating increased.
조홍현(Honghyun Cho) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
Recently, many plants use a lot of energy and various efforts are being made to reduce it. Techniques for reducing heat energy used in plants and improving heat transfer performance in the heat exchanger are being applied. Some methods for improving heat transfer in the heat exchanger including heat transfer improvement through changes in the structure and shape of the heat exchanger and improvement through enhancement of thermal properties of the working fluid. When the thermal properties of the working fluid are improved by using various ionic liquids, the performance of heat transfer can be improved. In this review, performance improvement technology using these ionic liquids is presented.